These days, everyone is trying to work smarter, not harder. In nursery production the way to work smarter is to tank mix.
Tank mixing is combining two or more crop production chemicals (pesticides, fertilizers, etc.) in one tank for application at the same time. Is tank mixing really a smart practice? Yes, if you're careful. Many products are available and so many combinations can be mixed that it would be naive to think that all of them work or that labels cover every possibility. Understanding what incompatibility is, how to recognize it, and why it happens can help you avoid nasty situations.
Signs of incompatibility
Incompatibility occurs when one component chemically reacts with or adversely affects one of more components of a tank mix. Incompatibility results in a product combination that is not usable, safe or effective. To spot incompatibility, look for these signs that may occur individually or combined:
- Heat
- Precipitates - flakes/crystals
- Gas bubbles
- Color change
- Surface scum or foam
- Oily droplets
- Gels or sludge
- Layering/separation line
Heat, precipitates, bubbles and color change generally indicate a chemical incompatibility between products. A reaction is occurring at the chemical level that is altering the original products. Scum or foam, oily droplets, gels, sludge and separation lines (like oil and water) generally indicate a physical incompatibility between products. Products won't mix together or if they do, they don't mix evenly or they separate from each other in a short time. In cases of physical incompatibility, an incompatibility agent can sometimes be added to the tank mix to correct the problem. An example is adding dish detergent to a mixture of oil and water, where the detergent keeps the oil mixed more evenly in the water and for a longer period of time.
Why didn't it work?
You may have been mixing the same products the same way you have for years, and for some reason, this time they're incompatible. Many factors influence whether or not a tank mix is incompatible. (Some of them you can control and some of them you can't).
- Wrong mixing order. Check the product labels for mixing instructions. When in doubt, use the jar test mixing order.
- Not enough water used. Start with a 1/3 to a 1/2 tank of water before adding any products, or mix a product in a couple of gallons of water before adding it to the tank. Sometimes products mix better when they are more dilute.
- Water tank or tank mix too acidic or basic (pH 5-7 is best) can cause incompatibility. Also, the tank mix itself can become too acidic or too basic. Sometimes water-soluble bags or packets will not dissolve in highly acidic or basic conditions.
- Delayed application. The longer a tank mix sits before application, the more potential there is for chemical reactions to occur or for products to separate out of the mix. Apply tank mixes as soon as possible after mixing.
- Temperatures too high or too low. If it's too hot or too cold for you to comfortably make an application, then it's probably not a good idea to be mixing products.
- Insufficient agitation. Sometimes the mixing process and the motion of the application vehicle are not sufficient to keep products mixed. This is especially true when dealing with mixes that require incompatibility agents or when dealing with long application times.
- Physical properties of products. Sometimes products just don't mix well. For example, one material may not form a solution or remain in solution when another is present. This happens frequently when mixing emulsifiable concentrates and wettable powders. While product active ingredients may not be incompatible, product formulations can be.
- Chemical properties of products. Incompatibility can results because product ingredients react chemically to form new substances. Chances of this increase when mixing products from different pesticide categories - for example, an insecticide mixed with a fungicide or a herbicide mixed with an insecticide.
- Application equipment. Incompatibility between galvanized application equipment and certain tank mixes can occur. Some tank mixes can corrode spray nozzles or cause hoses and seals to degrade.
Problems caused by incompatibility
Pesticide incompatibility can result in problems that can be detrimental to the crop, the equipment or the applicator.
- Increased phytotoxicity. The tank mix is "hot" and causes more injury to the target pest than expected or causes injury to the crop.
- Decreased effectiveness. A reaction occurs causing the products in the mix to become less effective or ineffective.
- Damage to application equipment. Equipment can become clogged, corroded or degraded. This results in improper application and expensive repairs or replacements.
- Injury to applicator. Proper safety precautions should be taken any time multiple products are mixed. Wear all recommended protective equipment. In addition, consider wearing eye and face protection and a heavy-duty pesticide-resistant apron if not already recommended.
- Increased residues. Product mixes can leave residues that take longer to break down or residues that discolor the crop, clothing or equipment.
- Expensive products are wasted. Any time incompatibility occurs and you can't make an application, it costs time, labor and, in some cases, expensive products.
- Disposal problems. New and possibly unstable chemicals can be the result of tank mix incompatibility. In large quantities these new chemicals can cause handling and disposal problems.
Know the signs of incompatibility. When tank mixing anything, keep in mind the factors that can influence incompatibility. When the label doesn't say "When mixing a combination of ...," do a jar test.
Jar test mixing order
To complete a jar test, follow these instructions. Put some water in a jar and add products in this order:
- Wettable powders (mix with water to form slurry then add).
- Water-dispersible granules.
- Dry flowables.
- Liquids (water-based solutions, surfactants).
- Emulsifiable concentrates.
- Solubles and adjuvants (crop oil, anti-foaming or drift agents).
Shake the jar for 10 seconds after adding each component. After the final component is added, shake the jar for 10 seconds and let it stand for 15-30 minutes. Check for signs of incompatibility. If incompatibility occurs, try using a compatibility agent. Add the compatibility agent first, then add the pesticides (or fertilizers/minerals) in the above order. If no signs of incompatibility occur, test the mixture on a small area before using on a large scale.
Precautions and savings
Tank mixes are a great way to work smarter for many reasons. They can provide better control than either product alone, and sometimes at lower application rates. They can also increase the length of product residual and the spectrum of pest control. Avoid long-term use of tank mixes of products from the same category to avoid resistance problems. And finally, if you have never experienced tank mix incompatibility, consider yourself lucky
